The present invention generally relates to the field of sealed batteries and more particularly to explosion-proof, safety features of a closure assembly incorporated in hermetically sealed secondary batteries such as lithium ion secondary batteries.
There has been a rapid increase in portable, cordless electric appliances of audiovisual equipment, office equipment such as personal computers, and communications equipment in recent years. Since non-aqueous electrolyte secondary batteries typically represented by high-capacity alkaline rechargeable batteries or lithium ion secondary batteries are ideally suited as a drive power source for such equipment, research is being conducted to develop a sealed non-aqueous electrolyte secondary battery of high energy density and excellent load characteristics.
One example of prior art closure assemblies for sealed batteries is shown in FIG. 19 to FIG. 21. In these figures, reference numeral 110, 120, 130 represent a metal cap, a metal spacer, and an upper metal foil, respectively. The center of the upper metal foil 130 is warped to form a dent 131, and a thin part 132 is formed by impressing on one side relative to this dent 131, as shown in FIG. 21. 140 is a dish-like insulating gasket having a bottom, and 150 is a belt-like lower metal foil. The lower metal foil 150 has a bulge 151 in its center, a slit 152 in the form of letter C surrounding the bulge 151, and punched holes 153 at both ends of the slit 152, as shown in FIG. 20. 160 is a metal case in the form of a cup which has a gas vent 161 in its center and is joined to a lead terminal that is connected to one electrode. The closure assembly for sealed batteries constructed as described above is mounted airtightly to an open end of an outer case of the battery. In the case of the closure assembly for sealed batteries described above, the upper and lower metal foils 130, 150 are electrically connected only through a welding point S in their respective centers, and the breaking strength of an uncut portion formed by the slit 152 in the lower metal foil determines the pressure at which this electrical connection is broken. Specifically, when the internal pressure of the battery which acts on the upper metal foil 130 through the punched holes 153 builds up to a predetermined value, the pressure concentrates on the warped portion 131 of the upper metal foil 130, pushing same upwards and thereby inverting the dent into a bulge as shown by a phantom line in FIG. 19. The welding point S of the lower metal foil 150 is thus pulled up, splitting apart the uncut portion of the slit 152 and thereby disconnecting the upper metal foil 130 and lower metal foil 150. The contact between the lower metal foil 150 connected to an electrode through the metal case 160 and the upper metal foil 130 connected to the metal cap 110 through the metal spacer 120 is broken whereby electric current supply is stopped. A further build-up of internal pressure leads to rupture of the thin part 132 in the upper metal foil 130, through which the gas within the battery is released to the outside.
In the event of failure, over-charging or inappropriate use of the charger and alike, pressure can build up within the battery to an excessive level due to an abnormal increase of gas generated by chemical reaction within the battery.
The battery can eventually explode or damage the equipment to which it is applied. To avert such possibility, explosion-proof features are normally provided in this and other types of batteries to release gas to the outside in case of build-up of pressure within the battery beyond some predetermined limit.
Furthermore, since there is a risk of ignition upon rapid heating of the battery in non-aqueous electrolyte secondary batteries, safety features are also provided by which power supply is stopped prior to emission of the gas in case the internal pressure of the battery exceeds a predetermined limit.
In the prior art closure assembly for sealed batteries described above, due to difficulty in controlling the machining precision of the thin part 132 in the upper metal foil 130, there exists variation in the thin part 132. As a result, the breaking pressure at the point of letting out the internal gas cannot be fixedly determined. The breaking pressure at the point when power supply is stopped is not constant either, because of the variation in dimensions of the warped portion 131 in the upper metal foil 130 and uncut portion of the slit 152 due to difficulty in controlling the machining precision. Improvement in the reliability of the explosion-proof, safety features is thus strongly desired. Furthermore, since the upper and lower metal foils 130, 150 are thin films, minute cracks that can cause leakage are inevitably formed in the welding point S where the upper and lower metal foils 130, 150 are laser-welded. Moreover, a considerable space in upward and downward directions is required in order to allow the warped portion 131 of the upper metal foil 130 to be inverted, by which the dimensions of the entire closure assembly cannot be further reduced.
An object of the present invention is to solve the aforementioned problems, i.e., to improve the reliability of safety features of sealed batteries for averting explosion. Another object of the invention is to make the closure assembly thinner while improving its leakage-proof performance.
In order to accomplish the above objects, the present invention according to a first feature thereof provides a closure assembly for sealed batteries characterized in that a pressure receiving sheet that consists of a resin sheet or a metal foil and is arranged in the closure assembly has a pressure receiving portion defined in one part of the pressure receiving sheet, and the periphery of said pressure receiving portion is restricted by other elements constituting the closure assembly that are positioned above and below the pressure receiving sheet, so that, upon an abnormal increase in pressure within the battery, the pressure receiving portion of the pressure receiving sheet expands and eventually ruptures for releasing gas within the battery to the outside.
With the above construction, it is easier to control the thickness and area of the pressure receiving portion of the pressure receiving sheet at a predetermined value than to control the thickness of the thin part in the upper metal foil at a predetermined value in the prior art example. There is thus less variation in the breaking pressure, and the reliability of the explosion-proof safety features for releasing gas upon an abnormal build-up of internal pressure can be improved.
The present invention according to a second feature thereof provides a closure assembly for sealed batteries characterized in that an insulating resin gasket in the closure assembly is shaped in a dish-like form having a bottom and is provided with a thin part in the bottom thereof, said thin part being defined to be a pressure receiving portion, and the periphery of said pressure receiving portion of the insulating resin gasket is restricted by other elements constituting the closure assembly that are positioned above the periphery of the pressure receiving portion, so that, upon an abnormal increase in pressure within the battery, the pressure receiving portion of the insulating resin gasket expands and eventually ruptures for releasing gas within the battery to the outside.
With the above construction, similarly to the first feature of the present invention, the reliability of the explosion-proof safety features for releasing gas upon an abnormal build-up of internal pressure can be improved, and, the construction can be simplified since the resin sheet in the first feature of the present invention is omitted.
The present invention according to a third feature thereof provides a closure assembly for sealed batteries characterized by having an insulating resin sheet and a thin metal sheet positioned above the insulating resin sheet and provided with a rupture portion, said insulating resin sheet and thin metal sheet being laid over one another within the closure assembly, wherein the insulating resin sheet has a pressure receiving portion defined in one part of the insulating resin sheet, and the insulating resin sheet and thin metal sheet stacked on the insulating resin sheet are restricted at a position surrounding the pressure receiving portion by other elements constituting the closure assembly that are positioned above and below the insulating resin sheet and thin metal sheet, said rupture portion of the thin metal sheet being positioned above said pressure receiving portion, and an external electrode terminal of the battery is electrically connected to an internal electrode of the battery through the rupture portion of the thin metal sheet, so that, upon an abnormal increase in pressure within the battery, the pressure receiving portion of the insulating resin sheet expands, whereby the rupture portion of the thin metal sheet ruptures for breaking the electrical connection between the external electrode terminal and internal electrode of the battery.
With the above construction, since there is no need to provide a space in the closure assembly for allowing a warped portion of the upper metal foil to be inverted which was required in the prior art example, the closure assembly and the sealed battery itself can be made thinner. Unlike the prior art example, the rupture portion of the thin metal sheet does not have a welding point, and therefore the present invention exhibits better performance of preventing leakage of electrolyte. Moreover, as compared to the prior art example in which the warped portion of the upper metal foil is inverted, the breaking pressure at which the rupture portion breaks can be set precisely with less variation. As a result, the reliability of the explosion-proof safety features for cutting electricity supply when internal pressure builds up excessively can be improved.
The present invention according to a fourth feature thereof provides a closure assembly for sealed batteries characterized by having an insulating resin gasket shaped in a dish-like form having a bottom and provided with a thin part in the bottom thereof, said thin part being defined to be a pressure receiving portion, and a thin metal sheet having a rupture portion stacked upon the upper surface of the bottom of the insulating resin gasket, wherein the thin metal sheet is restricted at a position surrounding the pressure receiving portion by the insulating resin gasket and other elements constituting the closure assembly that are positioned above the thin metal sheet, said rupture portion of the thin metal sheet being positioned above said pressure receiving portion, and an external electrode terminal of the battery is electrically connected to an internal electrode of the battery through the rupture portion of the thin metal sheet, so that, upon an abnormal increase in pressure within the battery, the pressure receiving portion of the insulating resin sheet expands, whereby the rupture portion of the thin metal sheet ruptures for breaking the electrical connection between the external electrode terminal and internal electrode of the battery.
With the above construction, similarly to the third feature of the present invention, the sealed battery can be made thinner, and it exhibits better performance of preventing leakage of the electrolyte. The reliability of the explosion-proof safety features for cutting electricity supply when internal pressure builds up excessively can be improved, and, the construction can be simplified since the resin sheet in the third feature of the present invention is omitted.
The present invention according to a fifth feature thereof provides a closure assembly for sealed batteries characterized by having an insulating resin sheet and a thin metal sheet stacked on the insulating resin sheet, the thin metal sheet being provided with a rupture portion, wherein the insulating resin sheet has a pressure receiving portion defined in one part of the insulating resin sheet, and the insulating resin sheet and thin metal sheet stacked thereon are restricted at a position surrounding the pressure receiving portion by other elements constituting the closure assembly that are positioned above and below the insulating resin sheet and thin metal sheet, said rupture portion of the thin metal sheet being positioned above said pressure receiving portion, and an external electrode terminal of the battery is electrically connected to an internal electrode of the battery through the rupture portion of the thin metal sheet, so that, when pressure within the battery increases excessively and reaches a first predetermined limit, the pressure receiving portion of the insulating resin sheet expands, whereby the rupture portion of the thin metal sheet ruptures for breaking the electrical connection between the external electrode terminal and internal electrode of the battery, and when the pressure within the battery further increases and reaches a second predetermined limit, the pressure receiving portion bursts for releasing gas within the battery to the outside of the battery.
With the above construction, similarly to the above first and third features of the present invention, the reliability of the explosion-proof safety features for breaking electricity supply when internal pressure builds up excessively and reaches a first predetermined limit, and the reliability of the explosion-proof safety features for releasing gas when the internal pressure further increases and reaches a second predetermined limit can both be improved. In addition, the sealed battery can be made thinner, and the electrolyte leakage-proof performance can be also improved.
The present invention according to a sixth feature thereof provides a closure assembly for sealed batteries characterized by having an insulating resin gasket shaped in a dish-like form having a bottom and provided with a thin part in the bottom thereof, said thin part being defined to be a pressure receiving portion, and a thin metal sheet having a rupture portion stacked upon the upper surface of the bottom of the insulating resin gasket, wherein the thin metal sheet is restricted at a position surrounding the pressure receiving portion by the insulating resin gasket and other elements constituting the closure assembly that are positioned above the thin metal sheet, said rupture portion of the thin metal sheet being positioned above said pressure receiving portion, and an external electrode terminal of the battery is electrically connected to an internal electrode of the battery through the rupture portion of the thin metal sheet, so that, when pressure within the battery increases excessively and reaches a first predetermined limit, the pressure receiving portion of the insulating resin sheet expands, whereby the rupture portion of the thin metal sheet ruptures for breaking the electrical connection between the external electrode terminal and internal electrode of the battery, and when the pressure within the battery further increases and reaches a second predetermined limit, the pressure receiving portion bursts for releasing gas within the battery to the outside of the battery.
With the above construction, similarly to the above fifth feature of the present invention, the reliability of the explosion-proof safety features for breaking electricity supply when internal pressure builds up excessively and reaches a first predetermined limit, and the reliability of the explosion-proof safety features for releasing gas when the internal pressure further increases and reaches a second predetermined limit can both be improved. In addition, the sealed battery can be made thinner, and the electrolyte leakage-proof performance can be also improved. Moreover, the construction can be simplified since the resin sheet in the fifth feature of the present invention is omitted.
In each of the second, fourth, and sixth features of the present invention, the pressure receiving portion of the insulating resin gasket can be constituted by a thin part uniformly provided to the gasket body. However, it is preferable that the pressure receiving portion is made of a resin film formed separately from the gasket body, this resin film being joined to the bore of the gasket body.
By constituting the pressure receiving portion with a separate resin film, the pressure at which the pressure receiving portion bursts or at which the rupture portion breaks can be more precisely determined with less variation. The reliability of the explosion-proof safety features can be thereby further improved.
Furthermore, by forming the insulating resin gasket by injection molding with a resin film placed at a predetermined position between metal molds, the closure assembly for sealed battery which has highly reliable explosion-proof safety features can be efficiently manufactured.
Moreover, by using a resin which has a high barrier effect against transmission of internal gas for the resin film, the airproof performance can be maintained. Alternatively, if the resin film is composed of the same resin as that of the gasket body and a resin which has a high barrier effect against transmission of internal gas, these being laminated, not only the airproof performance can be maintained, but also the bonding performance between the resin film and gasket body can be improved.